Computers continue to evolve. Time has witnessed huge, lumbering computers give way to nimble and powerful desktop, laptop, and handheld computing devices. Computational power has increased on almost an exponential curve, while size and portability of computing devices have significantly reduced.
People, once shackled to their computers, now experience new-found freedom as cell phones, video games, calculators, positioning systems, and personal computing devices become increasingly capable.
Traditional notions of computing are being challenged. Telecommuting is now common. A person can retreat to the mountains, walk along a trout-filled stream, and still remain connected to the business world. A parent can cheer on the sidelines of a soccer game and still pack along a virtual workspace on a handheld device. Advances in wireless communication and satellite systems provide increasing flexibility.
Life-changing advances are anticipated as computers continue to evolve.
The present invention employs digital watermarking techniques to even further increase the applications and flexibility of computers and computer-assisted activities. In some embodiments, digital watermarking techniques are combined with handheld computing devices. In other embodiments, digital watermarking techniques are employed with a document and/or data management systems. In still other embodiments, digital watermarking system and methods provide convenience and computing enhancements.
Digital watermarking, a form of steganography, is the science of encoding physical and electronic objects with plural-bit digital data, in such a manner that the data is essentially hidden from human perception, yet can be recovered by computer analysis. In physical objects, the data may be encoded in the form of surface texturing, or printing. Such marking can be detected from optical scan data, e.g., from a scanner, optical reader, input device, digital camera, or web cam. In electronic objects (e.g., digital audio or imagery—including video), the data may be encoded as slight variations in sample values. Or, if the object is represented in a so-called orthogonal domain (also termed “non-perceptual,” e.g., MPEG, DCT, wavelet, etc.), the data may be encoded as slight variations in quantization values or levels. The assignee's U.S. Pat. No. 6,122,403 and U.S. application Ser. No. 09/503,881 (now U.S. Pat. No. 6,614,914) are illustrative of certain watermarking technologies. Artisans know many others.
Digital watermarking systems typically have two primary components: an encoder that embeds the watermark in a host media signal, and a decoder that detects and reads the embedded watermark from a signal suspected of containing a watermark (e.g., a suspect signal). The encoder embeds a watermark by altering the host media signal. The decoder component analyzes a suspect signal to detect whether a watermark is present. In applications where the watermark encodes information, the decoder extracts this information from the detected watermark.
The analysis of the detected data can be accomplished in various ways. Presently, most steganographic decoding relies on general purpose microprocessors that are programmed by suitable software instructions to perform the necessary analysis. Other arrangements, such as using dedicated hardware, reprogrammable gate arrays, or other techniques, can of course be used.
Determining orientation of embedded data can be discerned by reference to visual clues. For example, some objects include subliminal graticule data, or other calibration data, steganographically encoded with the embedded data to aid in determining orientation. Others objects can employ overt markings, either placed for that sole purpose (e.g. reference lines or fiducials), or serving another purpose as well (e.g. lines of text), to discern orientation. Edge-detection algorithms can also be employed to deduce the orientation of the object by reference to its edges.
In one example, subliminal graticule data can be sensed to identify the locations within the image data where the binary data is encoded. The nominal luminance of each patch before encoding (e.g., background shading on a document) is slightly increased or decreased to encode a binary “1” or “0.” The change is slight enough to be generally imperceptible to human observers, yet statistically detectable from the image data. Preferably, the degree of change is adapted to the character of the underlying image, with relatively greater changes being made in regions where the human eye is less likely to notice them. Each area thus encoded can convey plural bits of data (e.g., 16-256 bits).
One problem that arises in many watermarking applications is that of object or positioning corruption. If the object is reproduced, skewed, or distorted, in some manner such that the content presented for watermark decoding is not identical to the object as originally watermarked, then the decoding process may be unable to recognize and decode the watermark. To deal with such problems, the watermark can convey a reference signal. The reference signal is of such a character as to permit its detection even in the presence of relatively severe distortion. Once found, the attributes of the distorted reference signal can be used to quantify the content's distortion. Watermark decoding can then proceed—informed by information about the particular distortion present.
The assignee's U.S. application Ser. No. 09/503,881 (now U.S. Pat. No. 6,614,914) and Ser. No. 09/452,023 (now U.S. Pat. No. 6,408,082) detail certain reference signals, and processing methods, that permit such watermark decoding even in the presence of distortion. In some image watermarking embodiments, the reference signal comprises a constellation of quasi-impulse functions in the Fourier magnitude domain, each with pseudorandom phase. To detect and quantify the distortion, the watermark decoder converts the watermarked image to the Fourier magnitude domain and then performs a log polar resampling of the Fourier magnitude image. A generalized matched filter correlates the known orientation signal with the re-sampled watermarked signal to find the rotation and scale parameters providing the highest correlation. The watermark decoder performs additional correlation operations between the phase information of the known orientation signal and the watermarked signal to determine translation parameters, which identify the origin of the watermark message signal. Having determined the rotation, scale and translation of the watermark signal, the reader then adjusts the image data to compensate for this distortion, and extracts the watermark message signal as described above.
Such watermarking techniques, and many others known to those skilled in the art, may be suitably employed with the present invention.
The foregoing and other features and advantages of the present invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.